Unenveloped letter-size mailpieces prepared for machinable or automation mailings must be sealed or glued completely along all four sides (or unsealed edges) or cured (tabbed) to prevent an open edge from jamming high-speed processing equipment. Standards for tabbing folded self-mailers, booklets, or postcards are based on basis weight of paper stock used and the location of the folded or bound edge. As an alternative to tabs or wafer seals, the open edge of the length of single-sheet self-mailers and postcards, and specific booklet designs, may be continuously glued or spot glued.

Tabs, wafer seals, cellophane tape, or permanent glue (continuous or spot) must not interfere with recognition of the barcode, rate marking, postage identification, or required address information. In all cases additional tabs or seals may be used. Cellophane tape is not acceptable within the barcode clear zone. Tabs or wafer seals placed in the barcode clear zone must contain a paper face meeting the standards for background reflectance and, if the barcode is not preprinted by the mailer, the standards for water-based ink.